Adding a request counter to the snippets fetcher.

components/ntp_snippets/request_throttler.h

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef COMPONENTS_NTP_SNIPPETS_REQUEST_THROTTLER_H_
 #define COMPONENTS_NTP_SNIPPETS_REQUEST_THROTTLER_H_
 
 #include <string>
 
 #include "base/macros.h"
 
 class PrefRegistrySimple;
 class PrefService;
 
 namespace base {
 class HistogramBase;
 }  // namespace base
 
 namespace ntp_snippets {
 
-struct RequestTypeInfo;
-
 // Counts requests to external services, compares them to a daily quota, reports
 // them to UMA. In the application code, create one local instance for each type
 // of requests, identified by the RequestType. The request counter is based on:
 //  - daily quota from a variation param "quota_|type|" in the NTPSnippets trial
 //  - pref "ntp.request_throttler.|type|.count" to store the current counter,
 //  - pref "ntp.request_throttler.|type|.day" to store current day to which the
 //    current counter value applies.
 // Furthermore the counter reports to histograms:
 //  - "NewTabPage.RequestThrottler.RequestStatus_|type|" - status of each
 //  request;
 //  - "NewTabPage.RequestThrottler.PerDay_|type|" - the daily count of requests.
 //
 // Implementation notes: When extending this class for a new RequestType, please
 //  1) define in request_counter.cc in kRequestTypeInfo
 //     a) the string value for your |type| and
 //     b) constants for day/count prefs;
 //  2) define a new RequestThrottlerTypes histogram suffix in histogram.xml
 //     (with the same string value as in 1a)).
 class RequestThrottler {
  public:
   // Enumeration listing all current applications of the request counter.
   enum class RequestType {
     CONTENT_SUGGESTION_FETCHER
   };
 
-  RequestThrottler(PrefService* pref_service,
-                 RequestType type,
-                 int default_quota);
+  RequestThrottler(PrefService* pref_service, RequestType type);
 
   // Registers profile prefs for all RequestTypes. Called from browser_prefs.cc.
   static void RegisterProfilePrefs(PrefRegistrySimple* registry);
 
   // Returns whether quota is available for another request and reports this
   // information to UMA. Forced requests always return true -- should be only
   // used for requests initiated by the user (if it is safe to assume that all
   // users cannot generate an amount of requests we cannot handle).
   bool DemandQuotaForRequest(bool force_request);
 
  private:
+  friend class RequestThrottlerTest;
+  // Used internally for working with a RequestType.
+  struct RequestTypeInfo {
+    const char* name;
+    const char* count_pref;
+    const char* day_pref;
+    const int default_quota;
+  };
+
+  // The array of info entries - one per each RequestType.
+  static const RequestTypeInfo kRequestTypeInfo[1];
+
   // Also emits the PerDay histogram if the day changed.
   void ResetCounterIfDayChanged();
 
   const char* GetRequestTypeAsString() const;
 
   int GetCount() const;
   void SetCount(int count);
   int GetDay() const;
   void SetDay(int day);
   bool HasDay() const;
 
   PrefService* pref_service_;
   const RequestTypeInfo& type_info_;
 
   // It comes from a variation parameter or |default_quota| as a fallback.
   int quota_;
 
   // The histograms for reporting the requests of the given |type_|.
   base::HistogramBase* histogram_request_status_;
   base::HistogramBase* histogram_per_day_;
 
   DISALLOW_COPY_AND_ASSIGN(RequestThrottler);
 };
 
 }  // namespace ntp_snippets
 
 #endif  // COMPONENTS_NTP_SNIPPETS_REQUEST_THROTTLER_H_